In mobile telecommunications networks, data services are known that make it possible to establish a packet-switching data connection between a terminal device that is connected to a mobile telecommunications network and a data network coupled to a mobile telecommunications network such as, for example, the Internet. As a rule, such services employ a packet data connection that is established via a packet service such as, for instance, GPRS (General Radio Packet Service), EGPRS (Enhanced GPRS), packet data transmission in the UMTS (Universal Mobile Telecommunications System) or HSDPA (High Speed Downlink Packet Access) or HSPA (High Speed Packet Access).
To an increasing degree, data services of the above-mentioned type can also be used when roaming, i.e. in cases when subscribers do not sign in to their home network but rather to another, so-called, visited network. In order for services of the home network to be made available to the subscriber, the access to data networks during roaming can be configured in the form of a so-called home access. This means that the access to the data network is made via the home network of the subscriber. For this purpose, a data connection request is forwarded by a switching unit of the visited mobile telecommunications network to the home network, which then establishes the connection to the data network.
As a rule, the conditions for access to the data service, especially the fees incurred for the use of the service, depend on the mobile telecommunications network from which the subscriber accesses the data service. Thus, when the data service is accessed from a visited mobile telecommunications network abroad, the fees are usually higher than when the data service is accessed from a visited mobile telecommunications network within one's own country or from one's home network.
For subscribers, the conditions for using the data service can often only be found in the rate schedules of their mobile telecommunications provider. This is impractical for users since such rate schedules are often not available, and the interpretation of the rates can be difficult because of differentiated fee structures. Consequently, the mobile telecommunications provider is faced with the problem that subscribers often do not use data services because they are afraid of incurring high fees.